Once programmed, the CPU runs your program and not the bootloader, and you can't read the flash.

If you press the "ERASE" button a flag bit is erased inside a system register and that makes the bootloader start again (instead of your program), but I don't know if the flash memory is erased too. If not you can use bossac to read the flash memory again, but you have to try it to discover if its possible.